Up-scale BMP color components using Windows-compatible method

This allows tests to compare against native behavior under Windows

build/cmake/tests/gui/CMakeLists.txt

@@ -156,6 +156,7 @@ set(TEST_GUI_DATA
     image/32bpp_rgb_a0.ico
     image/badrle4.bmp
     image/rgb16-3103.bmp
+    image/rgb32-7187.bmp
     image/rle4-delta-320x240.bmp
     image/rle8-delta-320x240-expected.bmp
     image/rle8-delta-320x240.bmp

src/common/imagbmp.cpp

@@ -513,6 +513,19 @@ struct BMPDesc
     int rmask, gmask, bmask;
 };
 
+// This seems to be the method Windows uses for up-scaling color components.
+// It works well with 4 bits or more, not so well with less. But using it
+// allows tests to compare against native behavior under Windows.
+inline wxUint8 UpscaleTo8Bits(wxUint8 x, unsigned nbits)
+{
+    if (nbits < 8)
+    {
+        x <<= (8 - nbits);
+        x |= x >> nbits;
+    }
+    return x;
+}
+
 // Read the data in BMP format into the given image.
 //
 // The stream must be positioned at the start of the bitmap data
@@ -528,6 +541,7 @@ bool LoadBMPData(wxImage * image, const BMPDesc& desc,
 
     wxUint32 rmask = 0, gmask = 0, bmask = 0, amask = 0;
     unsigned rshift = 0, gshift = 0, bshift = 0, ashift = 0;
+    unsigned rbits = 0, gbits = 0, bbits = 0;
 
     BMPPalette cmapMono[2];
     BMPPalette* cmap = nullptr;
@@ -607,8 +621,6 @@ bool LoadBMPData(wxImage * image, const BMPDesc& desc,
     {
         if ( desc.comp == BI_BITFIELDS )
         {
-            int bit;
-
             rmask = desc.rmask;
             gmask = desc.gmask;
             bmask = desc.bmask;
@@ -624,28 +636,14 @@ bool LoadBMPData(wxImage * image, const BMPDesc& desc,
                 amask = 0xFF000000;
                 ashift = 24;
             }
-
-            // find shift amount (Least significant bit of mask)
-            for (bit = bpp-1; bit>=0; bit--)
-            {
-                if (bmask & (1 << bit))
-                    bshift = bit;
-                if (gmask & (1 << bit))
-                    gshift = bit;
-                if (rmask & (1 << bit))
-                    rshift = bit;
-            }
         }
         else if ( bpp == 16 )
         {
             rmask = 0x7C00;
             gmask = 0x03E0;
             bmask = 0x001F;
-            rshift = 10;
-            gshift = 5;
-            bshift = 0;
         }
-        else if ( bpp == 32 )
+        else // bpp == 32
         {
             rmask = 0x00FF0000;
             gmask = 0x0000FF00;
@@ -653,10 +651,23 @@ bool LoadBMPData(wxImage * image, const BMPDesc& desc,
             amask = 0xFF000000;
 
             ashift = 24;
-            rshift = 16;
-            gshift = 8;
-            bshift = 0;
         }
+
+        // Determine shift counts and move masks to low byte,
+        // discarding lowest bits of any mask with more than 8 bits
+        for (; rmask && ((rmask & 1) == 0 || rmask > 0xff); rmask >>= 1)
+            rshift++;
+        for (; gmask && ((gmask & 1) == 0 || gmask > 0xff); gmask >>= 1)
+            gshift++;
+        for (; bmask && ((bmask & 1) == 0 || bmask > 0xff); bmask >>= 1)
+            bshift++;
+        // Count mask bits
+        for (; rmask; rmask >>= 1)
+            rbits++;
+        for (; gmask; gmask >>= 1)
+            gbits++;
+        for (; bmask; bmask >>= 1)
+            bbits++;
     }
 
     // RLE-compressed bitmaps do not necessarily specify every pixel explicitly,
@@ -918,20 +929,15 @@ bool LoadBMPData(wxImage * image, const BMPDesc& desc,
             }
             else if ( bpp == 16 )
             {
-                unsigned char temp;
                 wxUint16 aWord;
                 if ( !stream.ReadAll(&aWord, 2) )
                     return false;
                 wxUINT16_SWAP_ON_BE_IN_PLACE(aWord);
                 linepos += 2;
 
-                // scale color components to 8 bits
-                temp = rmask ? (aWord & rmask) * 255 / rmask : 0;
-                ptr[poffset] = temp;
-                temp = gmask ? (aWord & gmask) * 255 / gmask : 0;
-                ptr[poffset + 1] = temp;
-                temp = bmask ? (aWord & bmask) * 255 / bmask : 0;
-                ptr[poffset + 2] = temp;
+                ptr[poffset    ] = UpscaleTo8Bits(aWord >> rshift, rbits);
+                ptr[poffset + 1] = UpscaleTo8Bits(aWord >> gshift, gbits);
+                ptr[poffset + 2] = UpscaleTo8Bits(aWord >> bshift, bbits);
                 column++;
             }
             else
@@ -943,12 +949,9 @@ bool LoadBMPData(wxImage * image, const BMPDesc& desc,
 
                 wxUINT32_SWAP_ON_BE_IN_PLACE(aDword);
                 linepos += 4;
-                temp = (unsigned char)((aDword & rmask) >> rshift);
-                ptr[poffset] = temp;
-                temp = (unsigned char)((aDword & gmask) >> gshift);
-                ptr[poffset + 1] = temp;
-                temp = (unsigned char)((aDword & bmask) >> bshift);
-                ptr[poffset + 2] = temp;
+                ptr[poffset    ] = UpscaleTo8Bits(aDword >> rshift, rbits);
+                ptr[poffset + 1] = UpscaleTo8Bits(aDword >> gshift, gbits);
+                ptr[poffset + 2] = UpscaleTo8Bits(aDword >> bshift, bbits);
                 if ( alpha )
                 {
                     temp = (unsigned char)((aDword & amask) >> ashift);

tests/Makefile.in

@@ -599,7 +599,7 @@ data-image-sample:
 
 data-images: 
 	@mkdir -p image
-	@for f in bitfields.bmp bitfields-alpha.bmp 8bpp-colorsused-large.bmp 8bpp-colorsused-negative.bmp 32bpp_rgb.bmp 32bpp_rgb.ico 32bpp_rgb_a0.ico badrle4.bmp rgb16-3103.bmp rle4-delta-320x240.bmp rle8-delta-320x240.bmp rle8-delta-320x240-expected.bmp horse_grey.bmp horse_grey_flipped.bmp horse_rle4.bmp horse_rle4_flipped.bmp horse_rle8.bmp horse_rle8_flipped.bmp horse_bicubic_50x50.png horse_bicubic_100x100.png horse_bicubic_150x150.png horse_bicubic_300x300.png horse_bilinear_50x50.png horse_bilinear_100x100.png horse_bilinear_150x150.png horse_bilinear_300x300.png horse_box_average_50x50.png horse_box_average_100x100.png horse_box_average_150x150.png horse_box_average_300x300.png cross_bicubic_256x256.png cross_bilinear_256x256.png cross_box_average_256x256.png cross_nearest_neighb_256x256.png paste_input_background.png paste_input_black.png paste_input_overlay_transparent_border_opaque_square.png paste_input_overlay_transparent_border_semitransparent_circle.png paste_input_overlay_transparent_border_semitransparent_square.png paste_result_background_plus_circle_plus_square.png paste_result_background_plus_overlay_transparent_border_opaque_square.png paste_result_background_plus_overlay_transparent_border_semitransparent_square.png paste_result_no_background_square_over_circle.png wx.png toucan.png toucan_hue_0.538.png toucan_sat_-0.41.png toucan_bright_-0.259.png toucan_hsv_0.538_-0.41_-0.259.png toucan_light_46.png toucan_dis_240.png toucan_grey.png toucan_mono_255_255_255.png width-times-height-overflow.bmp width_height_32_bit_overflow.pgm bad_truncated.gif; do \
+	@for f in bitfields.bmp bitfields-alpha.bmp 8bpp-colorsused-large.bmp 8bpp-colorsused-negative.bmp 32bpp_rgb.bmp 32bpp_rgb.ico 32bpp_rgb_a0.ico badrle4.bmp rgb16-3103.bmp rgb32-7187.bmp rle4-delta-320x240.bmp rle8-delta-320x240.bmp rle8-delta-320x240-expected.bmp horse_grey.bmp horse_grey_flipped.bmp horse_rle4.bmp horse_rle4_flipped.bmp horse_rle8.bmp horse_rle8_flipped.bmp horse_bicubic_50x50.png horse_bicubic_100x100.png horse_bicubic_150x150.png horse_bicubic_300x300.png horse_bilinear_50x50.png horse_bilinear_100x100.png horse_bilinear_150x150.png horse_bilinear_300x300.png horse_box_average_50x50.png horse_box_average_100x100.png horse_box_average_150x150.png horse_box_average_300x300.png cross_bicubic_256x256.png cross_bilinear_256x256.png cross_box_average_256x256.png cross_nearest_neighb_256x256.png paste_input_background.png paste_input_black.png paste_input_overlay_transparent_border_opaque_square.png paste_input_overlay_transparent_border_semitransparent_circle.png paste_input_overlay_transparent_border_semitransparent_square.png paste_result_background_plus_circle_plus_square.png paste_result_background_plus_overlay_transparent_border_opaque_square.png paste_result_background_plus_overlay_transparent_border_semitransparent_square.png paste_result_no_background_square_over_circle.png wx.png toucan.png toucan_hue_0.538.png toucan_sat_-0.41.png toucan_bright_-0.259.png toucan_hsv_0.538_-0.41_-0.259.png toucan_light_46.png toucan_dis_240.png toucan_grey.png toucan_mono_255_255_255.png width-times-height-overflow.bmp width_height_32_bit_overflow.pgm bad_truncated.gif; do \
 	if test ! -f image/$$f -a ! -d image/$$f ; \
 	then x=yep ; \
 	else x=`find $(srcdir)/image/$$f -newer image/$$f -print` ; \

tests/image/image.cpp

@@ -1409,6 +1409,8 @@ TEST_CASE_METHOD(ImageHandlersInit, "wxImage::BMPLoadMethod", "[image][bmp]")
     CompareBMPImageLoad("image/horse_grey.bmp");
     CompareBMPImageLoad("image/horse_rle8.bmp");
     CompareBMPImageLoad("image/horse_rle4.bmp");
+    CompareBMPImageLoad("image/rgb16-3103.bmp");
+    CompareBMPImageLoad("image/rgb32-7187.bmp");
     CompareBMPImageLoad("image/rle8-delta-320x240.bmp",
         wxIMAGE_HAVE_DELTA_RLE_BITMAP);
     CompareBMPImageLoad("image/rle4-delta-320x240.bmp",
@@ -1647,11 +1649,6 @@ TEST_CASE_METHOD(ImageHandlersInit, "wxImage::BMP", "[image][bmp]")
         REQUIRE(image.LoadFile("image/32bpp_rgb_a0.ico", wxBITMAP_TYPE_ICO));
         REQUIRE_FALSE(image.GetAlpha());
     }
-    SECTION("bitfields")
-    {
-        REQUIRE(image.LoadFile("image/rgb16-3103.bmp", wxBITMAP_TYPE_BMP));
-        REQUIRE(image.GetData()[0] == 0xff);
-    }
 }
 
 TEST_CASE_METHOD(ImageHandlersInit, "wxImage::Paste", "[image][paste]")

tests/makefile.gcc

@@ -574,7 +574,7 @@ data-image-sample:
 
 data-images: 
 	if not exist image mkdir image
-	for %%f in (bitfields.bmp bitfields-alpha.bmp 8bpp-colorsused-large.bmp 8bpp-colorsused-negative.bmp 32bpp_rgb.bmp 32bpp_rgb.ico 32bpp_rgb_a0.ico badrle4.bmp rgb16-3103.bmp rle4-delta-320x240.bmp rle8-delta-320x240.bmp rle8-delta-320x240-expected.bmp horse_grey.bmp horse_grey_flipped.bmp horse_rle4.bmp horse_rle4_flipped.bmp horse_rle8.bmp horse_rle8_flipped.bmp horse_bicubic_50x50.png horse_bicubic_100x100.png horse_bicubic_150x150.png horse_bicubic_300x300.png horse_bilinear_50x50.png horse_bilinear_100x100.png horse_bilinear_150x150.png horse_bilinear_300x300.png horse_box_average_50x50.png horse_box_average_100x100.png horse_box_average_150x150.png horse_box_average_300x300.png cross_bicubic_256x256.png cross_bilinear_256x256.png cross_box_average_256x256.png cross_nearest_neighb_256x256.png paste_input_background.png paste_input_black.png paste_input_overlay_transparent_border_opaque_square.png paste_input_overlay_transparent_border_semitransparent_circle.png paste_input_overlay_transparent_border_semitransparent_square.png paste_result_background_plus_circle_plus_square.png paste_result_background_plus_overlay_transparent_border_opaque_square.png paste_result_background_plus_overlay_transparent_border_semitransparent_square.png paste_result_no_background_square_over_circle.png wx.png toucan.png toucan_hue_0.538.png toucan_sat_-0.41.png toucan_bright_-0.259.png toucan_hsv_0.538_-0.41_-0.259.png toucan_light_46.png toucan_dis_240.png toucan_grey.png toucan_mono_255_255_255.png width-times-height-overflow.bmp width_height_32_bit_overflow.pgm bad_truncated.gif) do if not exist image\%%f copy .\image\%%f image
+	for %%f in (bitfields.bmp bitfields-alpha.bmp 8bpp-colorsused-large.bmp 8bpp-colorsused-negative.bmp 32bpp_rgb.bmp 32bpp_rgb.ico 32bpp_rgb_a0.ico badrle4.bmp rgb16-3103.bmp rgb32-7187.bmp rle4-delta-320x240.bmp rle8-delta-320x240.bmp rle8-delta-320x240-expected.bmp horse_grey.bmp horse_grey_flipped.bmp horse_rle4.bmp horse_rle4_flipped.bmp horse_rle8.bmp horse_rle8_flipped.bmp horse_bicubic_50x50.png horse_bicubic_100x100.png horse_bicubic_150x150.png horse_bicubic_300x300.png horse_bilinear_50x50.png horse_bilinear_100x100.png horse_bilinear_150x150.png horse_bilinear_300x300.png horse_box_average_50x50.png horse_box_average_100x100.png horse_box_average_150x150.png horse_box_average_300x300.png cross_bicubic_256x256.png cross_bilinear_256x256.png cross_box_average_256x256.png cross_nearest_neighb_256x256.png paste_input_background.png paste_input_black.png paste_input_overlay_transparent_border_opaque_square.png paste_input_overlay_transparent_border_semitransparent_circle.png paste_input_overlay_transparent_border_semitransparent_square.png paste_result_background_plus_circle_plus_square.png paste_result_background_plus_overlay_transparent_border_opaque_square.png paste_result_background_plus_overlay_transparent_border_semitransparent_square.png paste_result_no_background_square_over_circle.png wx.png toucan.png toucan_hue_0.538.png toucan_sat_-0.41.png toucan_bright_-0.259.png toucan_hsv_0.538_-0.41_-0.259.png toucan_light_46.png toucan_dis_240.png toucan_grey.png toucan_mono_255_255_255.png width-times-height-overflow.bmp width_height_32_bit_overflow.pgm bad_truncated.gif) do if not exist image\%%f copy .\image\%%f image
 
 en_GB: 
 	if not exist $(OBJS)\intl\en_GB mkdir $(OBJS)\intl\en_GB

tests/makefile.vc

@@ -875,7 +875,7 @@ data-image-sample:
 
 data-images: 
 	if not exist image mkdir image
-	for %f in (bitfields.bmp bitfields-alpha.bmp 8bpp-colorsused-large.bmp 8bpp-colorsused-negative.bmp 32bpp_rgb.bmp 32bpp_rgb.ico 32bpp_rgb_a0.ico badrle4.bmp rgb16-3103.bmp rle4-delta-320x240.bmp rle8-delta-320x240.bmp rle8-delta-320x240-expected.bmp horse_grey.bmp horse_grey_flipped.bmp horse_rle4.bmp horse_rle4_flipped.bmp horse_rle8.bmp horse_rle8_flipped.bmp horse_bicubic_50x50.png horse_bicubic_100x100.png horse_bicubic_150x150.png horse_bicubic_300x300.png horse_bilinear_50x50.png horse_bilinear_100x100.png horse_bilinear_150x150.png horse_bilinear_300x300.png horse_box_average_50x50.png horse_box_average_100x100.png horse_box_average_150x150.png horse_box_average_300x300.png cross_bicubic_256x256.png cross_bilinear_256x256.png cross_box_average_256x256.png cross_nearest_neighb_256x256.png paste_input_background.png paste_input_black.png paste_input_overlay_transparent_border_opaque_square.png paste_input_overlay_transparent_border_semitransparent_circle.png paste_input_overlay_transparent_border_semitransparent_square.png paste_result_background_plus_circle_plus_square.png paste_result_background_plus_overlay_transparent_border_opaque_square.png paste_result_background_plus_overlay_transparent_border_semitransparent_square.png paste_result_no_background_square_over_circle.png wx.png toucan.png toucan_hue_0.538.png toucan_sat_-0.41.png toucan_bright_-0.259.png toucan_hsv_0.538_-0.41_-0.259.png toucan_light_46.png toucan_dis_240.png toucan_grey.png toucan_mono_255_255_255.png width-times-height-overflow.bmp width_height_32_bit_overflow.pgm bad_truncated.gif) do if not exist image\%f copy .\image\%f image
+	for %f in (bitfields.bmp bitfields-alpha.bmp 8bpp-colorsused-large.bmp 8bpp-colorsused-negative.bmp 32bpp_rgb.bmp 32bpp_rgb.ico 32bpp_rgb_a0.ico badrle4.bmp rgb16-3103.bmp rgb32-7187.bmp rle4-delta-320x240.bmp rle8-delta-320x240.bmp rle8-delta-320x240-expected.bmp horse_grey.bmp horse_grey_flipped.bmp horse_rle4.bmp horse_rle4_flipped.bmp horse_rle8.bmp horse_rle8_flipped.bmp horse_bicubic_50x50.png horse_bicubic_100x100.png horse_bicubic_150x150.png horse_bicubic_300x300.png horse_bilinear_50x50.png horse_bilinear_100x100.png horse_bilinear_150x150.png horse_bilinear_300x300.png horse_box_average_50x50.png horse_box_average_100x100.png horse_box_average_150x150.png horse_box_average_300x300.png cross_bicubic_256x256.png cross_bilinear_256x256.png cross_box_average_256x256.png cross_nearest_neighb_256x256.png paste_input_background.png paste_input_black.png paste_input_overlay_transparent_border_opaque_square.png paste_input_overlay_transparent_border_semitransparent_circle.png paste_input_overlay_transparent_border_semitransparent_square.png paste_result_background_plus_circle_plus_square.png paste_result_background_plus_overlay_transparent_border_opaque_square.png paste_result_background_plus_overlay_transparent_border_semitransparent_square.png paste_result_no_background_square_over_circle.png wx.png toucan.png toucan_hue_0.538.png toucan_sat_-0.41.png toucan_bright_-0.259.png toucan_hsv_0.538_-0.41_-0.259.png toucan_light_46.png toucan_dis_240.png toucan_grey.png toucan_mono_255_255_255.png width-times-height-overflow.bmp width_height_32_bit_overflow.pgm bad_truncated.gif) do if not exist image\%f copy .\image\%f image
 
 en_GB: 
 	if not exist $(OBJS)\intl\en_GB mkdir $(OBJS)\intl\en_GB

tests/test.bkl

@@ -384,6 +384,7 @@
             32bpp_rgb_a0.ico
             badrle4.bmp
             rgb16-3103.bmp
+            rgb32-7187.bmp
             rle4-delta-320x240.bmp
             rle8-delta-320x240.bmp
             rle8-delta-320x240-expected.bmp